The present invention relates to a multiline telephone apparatus having a caller ID signal detecting function.
Prior Art
Below is explained a conventional multiline telephone apparatus with a caller ID (bell core system) signal detecting function connected to a plurality of telephone lines.
First, the caller ID signal is described. As shown in FIG. 3, the caller ID signal is transmitted in a silent portion between first and second bell incoming signals as being modulated in FSK (frequency shift keying) system of CCITT V.23.
The caller ID signal is composed of a channel seizure signal which issues logic 1 (1200 Hz) and logic 0 (2200 Hz) alternately, a carrier signal portion holding logic 1 (1200 Hz) for 150 ms continuously, and a data signal portion of 175 ms showing caller""s telephone number, call time and other data. FIG. 3 is an example of signal upon bell incoming, but in voice mail service or the like, there is no bell incoming signal, and only the caller ID signal shown in FIG. 3 is transmitted.
FIG. 2 is a block diagram of a conventional multiline telephone apparatus with caller ID signal detecting function.
First, the operation of the voice system of the multiline telephone apparatus is explained. When the talk in telephone line B(1axe2x80x2-1bxe2x80x2) is selected by input means not shown, a switch 16 is set at lower (b) side, and by unhooking the handset, telephone line closing means 3 is turned on, and the handset talk circuit between the handset and the telephone line B is formed. The receiving sound signal from the telephone line B is transferred in the sequence of diode bridge 2xe2x80x2, switch 16, telephone line closing means 3, side tone suppression circuit 5, receiving amplifier 8, and handset speaker 10. The transmitting sound is transferred in the sequence of handset microphone 11, transmitting amplifier 9, line send-out amplifier 4, telephone line closing means 3, switch 16, and diode bridge 2xe2x80x2, and is sent out to the telephone line B.
The operation of the caller ID signal system is explained. Incoming signals from telephone line A(1a-1b) and telephone line B(1axe2x80x2-1bxe2x80x2) are put into coupling capacitors 6a and 6b, or 6axe2x80x2 and 6bxe2x80x2 where DC components of signals are cut off, and are amplified respectively in differential amplifiers 7, 7xe2x80x2, and put into caller ID demodulation modems 12, 12xe2x80x2. The caller ID signal of each telephone line is demodulated in the caller ID demodulation modems 12, 12xe2x80x2, and data of telephone number and others are output. The demodulated output data are put into a controller 17, and are displayed in LCD or other display device not shown.
Problems that the Invention is to Solve
However, such conventional multiline telephone apparatus with caller ID signal detecting function requires modems for caller ID demodulation in individual telephone lines. The modems are very expensive, which is a bottleneck for reduction of cost.
Some of the conventional multiline telephone apparatuses with caller ID signal detecting function employ a method of detecting the bell incoming signal, changing over the telephone line, and feeding into the modem in order to operate by one modem only. Recently, aside from the service of noticing the telephone number data by sending a caller ID signal between first and second bell incoming signals (FIG. 3), in the voice mail service, the voice mail data telling that the message has been recorded in the voice mail is sent only by using the caller ID signal regardless of the bell incoming signal. More recently, there is a caller ID service corresponding to call waiting to inform of a call from a third party during talk, and in this case, too, the caller ID signal is sent alone. Therefore, it is no longer possible to cope with the system of changing over the input to the modem by detecting the bell incoming signal.
The invention is intended to improve the subjects mentioned above, and it is hence an object thereof to present a multiline telephone apparatus capable of processing caller ID signals of a plurality of telephone lines by one demodulation modem alone.
Means of Solving the Problems
To achieve the object, the invention provides a multiline telephone apparatus having a plurality of caller ID signal detecting circuits for detecting the channel seizure signal or carrier signal in the caller ID signal, in order to change over a plurality of telephone line inputs to a caller ID demodulation modem.
The invention hence realizes a multiline telephone apparatus capable of processing caller ID signals of a plurality of telephone lines by one demodulation modem only.